Synchronized etalon filters

Abstract

A method for synchronizing an etalon to a preselected set of optical frequencies includes the step of generating a transmission spectrum for an etalon having a characteristic free spectral range that is a function of its effective length. The optical frequencies for the transmission spectrum are provided by two optical reference frequencies such as produced by a first and second frequency locked laser. The effective length of the etalon is set in relation to the optical reference frequencies.

I claim: 
     
       1. A method of synchronizing a Fabry-Perot etalon to a preselected set of optical frequencies, said method comprising the steps of: generating a first optical reference frequency with a first optical frequency reference and generating a second optical reference frequency distinct from said first optical reference frequency with a second optical frequency reference;   generating a transmission spectrum for an etalon having an effective length and a characteristic free spectral range that is a function of the effective length; and   varying the effective length of the etalon to vary the characteristic free spectral range until the etalon generates a particular mode substantially equal to the first optical reference frequency and another mode having a minimum offset from the second optical reference frequency, said particular and another modes generated by the etalon being a preselected number of modes apart.   
     
     
       2. The method of claim 1 wherein the etalon has an angular position with respect to an incident optical frequency and wherein the step of varying the effective length comprises the step of varying the angular position of the etalon with respect to the incident optical frequency. 
     
     
       3. The method of claim 2 wherein the step of varying the angular position of the etalon comprises: monitoring the transmission spectrum and fixing the angular position of the etalon when the amplitudes of the first and second optical reference frequencies are a maxima.   
     
     
       4. The method of claim 1 wherein said first and second optical frequency references are respectively provided by first and second frequency locked lasers. 
     
     
       5. The method of claim 4 wherein said first and second frequency locked lasers are locked to a first atomic transition in krypton occurring between 1s 2  and 2p 8  and a second atomic transition in krypton occurring between 2p 10  and 3d 3 , respectively 
     
     
       6. The method of claim 4 further comprising the steps of: providing a third frequency-locked laser locked to the one mode of the etalon;   generating a beat spectrum between the third frequency locked laser and the first frequency locked laser; and   further varying the angular position of the etalon until the beat frequency of the beat spectrum is substantially equal to zero.   
     
     
       7. The method of claim 1 wherein the transmission spectrum is generated by a broadband optical source. 
     
     
       8. A WDM optical communication system comprising: a Fabry-Perot etalon synchronized to a set of preselected optical frequencies by; providing a first optical frequency reference generating a first optical reference frequency and a second optical frequency reference generating a second optical reference frequency distinct from said first optical reference frequency; generating a transmission spectrum for an etalon having an effective length and a characteristic free spectral range that is a function of the effective length; and varying the effective length of the etalon to vary the characteristic free spectral range until the etalon generates a particular mode substantially equal to the first optical reference frequency and another mode having a minimum offset from the second optical reference frequency, said particular and another modes generated by the etalon being a preselected number of modes apart;   means for generating the preselected optical frequencies;     at least two optical transmitters each operating at a frequency equal to one of the preselected optical frequencies;   a multiplexer for multiplexing the frequencies generated by the at least two optical transmitters;   an optical transmission path for transmitting the multiplexed frequencies;   a demultiplexer for demultiplexing the multiplexed frequencies;   at least two receivers for receiving selected ones of the demultiplexed frequencies; and   means for maintaining the optical frequencies of the optical transmitters at the preselected optical frequencies of the Fabry-Perot etalon.   
     
     
       9. The etalon of claim 8 wherein the etalon has an angular position with respect to an incident optical frequency and wherein the step of varying the effective length comprises the step of varying the angular position of the etalon with respect to the incident optical frequency. 
     
     
       10. The etalon of claim 9 wherein the step of varying the angular position of the etalon comprises: monitoring the transmission spectrum and fixing the angular position of the etalon when the amplitudes of the first and second optical reference frequencies are a maxima.   
     
     
       11. The etalon of claim 9 wherein said first and second optical frequency references are respectively provided by first and second frequency locked lasers. 
     
     
       12. The etalon of claim 11 wherein said first and second frequency locked lasers are locked to a first atomic transition in krypton occurring between 1s 2  and 2p 8  and a second atomic transition in krypton occurring between 2p 10  and 3d 3 , respectively. 
     
     
       13. The etalon of claim 12 wherein the transmission spectrum is generated by a broadband optical source. 
     
     
       14. The etalon of claim 11 further comprising the steps of: providing a third frequency-locked laser locked to the one mode of the etalon;   generating a beat spectrum between the third frequency locked laser and the first frequency locked laser; and   further varying the angular position of the etalon until the beat frequency of the beat spectrum is substantially equal to zero.   
     
     
       15. A method of synchronizing a Fabry-Perot etalon to a preselected set of optical frequencies, said method comprising the steps of: generating a first optical reference frequency with a first optical frequency reference and generating a second optical reference frequency distinct from said first optical reference frequency with a second optical frequency reference;   generating a transmission spectrum for an etalon having an effective length and a characteristic free spectral range that is a function of the effective length; and   varying the effective length of the etalon to vary the characteristic free spectral range until the etalon generates a particular mode matching the first reference frequency and another mode matching the second optical reference frequency.   
     
     
       16. The method of claim 15 further comprising the step of preselecting the number of modes between said particular mode and said another mode of the etalon. 
     
     
       17. An etalon synchronized to a set of preselected optical frequencies by a method comprising: the steps of: providing a first optical frequency reference generating a first optical reference frequency and a second optical frequency reference generating a second optical reference frequency distinct from said first optical reference frequency;   generating a transmission spectrum for an etalon having an effective length and a characteristic free spectral range that is a function of the effective length; and   varying the effective length of the etalon to vary the characteristic free spectral range until the etalon generates a particular mode substantially equal to the first optical reference frequency and another mode having a minimum offset from the second optical reference frequency, said particular and another modes generated by the etalon being a preselected number of modes apart.   
     
     
       18. The etalon of claim 17 wherein the etalon has an angular position with respect to an incident optical frequency and wherein the step of varying the effective length comprises the step of varying the angular position of the etalon with respect to the incident optical frequency. 
     
     
       19. The etalon of claim 18 wherein the step of varying the angular position of the etalon comprises: monitoring the transmission spectrum and fixing the angular position of the etalon when the amplitudes of the first and second optical reference frequencies are a maxima.   
     
     
       20. The etalon of claim 17 wherein said first and second optical frequency references are respectively provided by first and second frequency locked lasers. 
     
     
       21. The etalon of claim 20 wherein said first and second frequency locked lasers are locked to a first atomic transition in krypton occurring between 1s 2  and 2p 8  and a second atomic transition in krypton occurring between 2p 10  and 3d 3 , respectively. 
     
     
       22. The etalon of claim 21 wherein the transmission spectrum is generated by a broadband optical source. 
     
     
       23. The etalon of claim 20 further comprising the steps of: providing a third frequency-locked laser locked to the one mode of the etalon;   generating a beat spectrum between the third frequency locked laser and the first frequency locked laser; and   further varying the angular position of the etalon until the beat frequency of the beat spectrum is substantially equal to zero.